Upwardly acting doors have conventionally been provided with a drawbar assembly connected between the driving carriage and the door. In many instances, the actual connection between the drawbar assembly and the door utilizes a spring box which enables compression of the springs therein when the door reaches a stationary position when moving in the closing direction, so as to permit limited continued movement of the drive carriage. However, the known drawbar assembly and associated spring box have not permitted simple adjustment in either the tension or compression of the spring. Further, these known devices have not readily compensated for the shock loads imposed on the drawbar assembly and the door when movement is initiated in the opening direction.
Accordingly, the present invention relates to an improved drawbar assembly for connection between the door and the drive carriage, which drawbar assembly incorporates springs therein which not only permit relative movement between the carriage and the door, such as when the door is stationary, but also permit this relative movement when the door is being moved in its opening direction so as to compensate for the shock loads imposed thereon during startup. In addition, the improved drawbar assembly of the present invention is structurally simple and yet permits its length and spring characteristics to be readily adjusted as desired.
Other objects and purposes of the invention will be apparent to persons familiar with this type of equipment upon reading the following specification and inspecting the accompanying drawings.